Surface Sputtering Research Articles

Trends of Sputtering Parameters in Monte Carlo Simulations of Rare Gas Impingement of GaSb, AlSb and InSb

Binary alloys of Group III-V metals and metalloids, such as GaSb, InSb and AlSb, were recently found to be very promising spintronic materials. For such potentially innovative materials, the quantum spin properties of constituent electrons can be exploited, for better enhanced high-tech applications, than the particulate dynamics of the electrons as in current electronic device applications. Ion beam surface sputtering is a versatile tool for crystal and thin film growth in materials science and characterisation. Consequently, trends of some sputtering parameters were investigated through Monte Carlo simulations of the bombardment of the binary compounds GaSb, InSb and AlSb using Argon, Helium and Krypton ions. The sputtering parameters for the binary compounds were found to be inconsistent as the angle of incidence increased, which occurred for different ion and energy combinations. Also, the maximum sputtering yield did not occur at a particular angle but within a range of values, 65° -85° and 75°- 85° for ion energies 1keV and 10keV respectively. The sputtering yield was also found to increase with an increase in the ion energy.

Sputtering of silicon surface by silver-ion implantation

The article describes the study of Si surface sputtering with the low-energy high-dose implantation by Ag+ ions with energy E = 30 keV and current density J = 8 μA/cm2. The radiation dose was D = 2.5 · 1016–1.5 · 1017 ion/cm2. It was found that the thickness of the spattered Ag:Si layer monotonously increased up to 50 nm when D reached its maximum, and the value of the effective sputtering yield was ~1.6.

Strengthening of cutting tools using beams of fast neutral atoms in a low-pressure gas discharge plasma

The surface of a 26-mm-diameter reamer made of AISI M2 high-speed steel has been nitrided in a low-pressure glow discharge plasma. Then a 3-μm-thick wear-resistant TiN coating has been magnetron sputtered on the hardened surface. After the combined processing the reamer’s cutting edges radii grew from the initial value of ∼8 μm up to ∼37 μm. The reason for the strengthened tool blunting is selective sputtering of the edges by heating ions accelerated from the plasma. Another reamer under nitriding was heated by a beam of fast atoms arriving at the tool surface from an immersed in the plasma concave grid negatively biased to 6 kV. Due to the uniform sputtering of the tool surface by the beam, the edges radii after nitriding and 3-μm-thick TiN coating deposition did not exceed the initial value.

Diagnostic mirrors for ITER: research in the frame of International Tokamak Physics Activity

Mirrors will be used as first plasma-viewing elements in optical and laser-based diagnostics in ITER. Deterioration of the mirror performance due to e.g. sputtering of the mirror surface by plasma particles or deposition of impurities will hamper the entire performance of the affected diagnostic and thus affect ITER operation. The Specialists Working Group on First Mirrors (FM SWG) in the Topical Group on Diagnostics of the International Tokamak Physics Activity (ITPA) plays an important role in finding solutions for diagnostic first mirrors.Sound progress in research and development of diagnostic mirrors in ITER was achieved since the last overview in 2009. Single crystal (SC) rhodium (Rh) mirrors became available. SC rhodium and molybdenum (Mo) mirrors survived in conditions corresponding to ~200 cleaning cycles with a negligible degradation of reflectivity. These results are important for a mirror cleaning system which is presently under development. The cleaning system is based on sputtering of contaminants by plasma. Repetitive cleaning was tested on several mirror materials. Experiments comprised contamination/cleaning cycles. The reflectivity SC Mo and Rh mirrors has changed insignificantly after 80 cycles. First in situ cleaning using radiofrequency (RF) plasma was conducted in EAST tokamak with a mock-up plate of ITER edge Thomson Scattering (ETS) with five inserted mirrors. Contaminants from the mirrors were removed. Physics of cleaning discharge was studied both experimentally and by modeling.Mirror contamination can also be mitigated by protecting diagnostic ducts. A deposition mitigation (DeMi) duct system was exposed in KSTAR. The real-time measurement of deposition in the diagnostic duct was pioneered during this experiment. Results evidenced the dominating effect of the wall conditioning and baking on contamination inside the duct. A baffled cassette with mirrors was exposed at the main wall of JET for 23,6 plasma hours. No significant degradation of reflectivity was measured on mirrors located in the ducts.Predictive modeling was further advanced. A model for the particle transport, deposition and erosion at the port-plug was used in selecting an optical layout of several ITER diagnostics. These achievements contributed to the focusing of the first mirror research thus accelerating the diagnostic development. Modeling requires more efforts. Remaining crucial issues will be in a focus of the future work of the FM SWG.

Atomic insight into concurrent He, D, and T sputtering and near-surface implantation of 3C-SiC crystallographic surfaces

Abstract We present results from atomistic simulations of sputtering and near-surface implantation of concurrent He, D, and T bombardment of cubic silicon carbide (3C-SiC). This is achieved by first establishing a many-body interatomic potential parameter set to treat interactions of He and hydrogenic species in 3C-SiC informed by ab-initio calculations. To obtain sputtering yields we perform both classical molecular dynamics and binary collision approximation simulations for normal incident particles having energies ranging from 25 to 800 eV. We find that due to differences in species surface binding energy of various crystallographic surfaces in 3C-SiC, the sputtering yield of Si is significantly less than that of C, but sputtering yields show limited sensitivity to crystallographic surface orientation. An exception to this occurs when the terminating crystallographic surface plane is more rich in Si rather than C, resulting in comparable sputtering yields of Si and C. The influence of temperature on sputtering is explored and shows limited effect. Finally, the nature of implanted He, D, and T within 3C-SiC surfaces is investigated to understand implantation profiles and stability of defects.

Modeling and Simulation of the Effect of Cathode Gas Flow on the Lifetime and Performance of an Annular-Geometry Ion Engine

The past measurements of the plasma density and potential profiles near the exit of the keeper electrode in a hollow cathode device suggested that turbulent ion acoustic fluctuations and ionization instability in the cathode plume significantly increased the energy of the ions that flow from this region. The lifetime of keeper electrode is limited by sputtering or ion bombardment of the Molybdenum surface exposed to the discharge plasma. Increases in the cathode gas flow reduce the amplitude of the fluctuations and the number and energy of the energetic ions, which decreases the erosion rate of the keeper electrodes. However, as the cathode gas flow is raised for a given discharge current, the performance of a 5-kW Annular-Geometry Ion Engine (AGI-Engine) declines. There is a strong relationship between the performance and the lifetime of the ion thruster. To validate whether the 20-A hollow cathode satisfied China's communication satellite platform's application requirement for North-South station keeping, this paper analyzed the effect of the cathode gas flow on the performance and the lifetime of the AGI-Engine. Different from the previous methods, this paper first tracked the movement of energetic ions generated in the plume of the hollow cathode, predicted erosion rates, found where they hit the keeper electrode, and then determined the amount of material that they sputtered. A review of past experimental results was presented first. Next, based on the existing experimental data, theoretical analysis and numerical calculations were performed to determine the optimum gas flow range and the performance curve of the 20-A hollow cathode. The results showed that the primary erosion mechanism of the keeper electrode was caused by impact from Charge Exchange Xenon (CEX) ions, which caused the cathode orifice to be widened and attenuated over time. However, heavy double xenon (X e ++ ) ions, which struck the keeper electrode more severely than CEX ions, were the most crucial factor that limited the lifetime of the 20-A hollow cathode due to their high energy and large mass.

Influence of heavier impurity deposition on surface morphology development and sputtering behavior explored in multiple linear plasma devices

Surface morphology development and sputtering behavior of Cr, as a test material, have been explored under He plasma exposure at a low incident ion energy of ∼80 eV in multiple linear plasma devices: PISCES-A, PSI-2, and NAGDIS-II. From comparison of the experiments in these devices, deposition of a small amount of heavier impurities (Mo in NAGDIS-II and Ta in PISCES-A) onto Cr is found to result in the formation of cone structures on the Cr surface due to preferential sputtering, resulting in a significant reduction (up to ∼10 times) in the sputtering yield of Cr due to line-of-sight redeposition onto the neighboring cones. The heavier impurities are thought to originate from a sample holding cap/cover, which can be sputtered by a trace amount of intrinsic impurities (C, O, etc) as well as by Cr ionized in the plasma. It can be concluded from the Cr experiments, as well as additional Be data collected in PISCES-B, that heavier impurity deposition plays a major role in the cone structure formation, while other mechanisms (e.g. surface irregularity and oxide) also exist.

Impact of Kr and Ar seeding on D retention in ferritic-martensitic steels after high-fluence plasma exposure

Total deuterium (D) retention from the bulk material of reduced-activation ferritic-martensitic (RAFM) steel Eurofer’97 (EU’97) and commercial ferritic-martensitic grade P92 was traced experimentally by means of thermal desorption spectroscopy (TDS) and linked to the role of krypton (Kr) and argon (Ar) seeding during high-fluence plasma exposure. The influence of impurity seeding on the steel microstructure was determined using scanning electron microscopy (SEM) and extended with focused ion beam (FIB) cross-sectioning. D capture at depths in the µm range was measured by nuclear reaction analysis (NRA). Plasma exposure of the steel samples occurred at 470 K with ion energy of 30–40 eV in the linear plasma device PSI-2 with up to 10% simultaneous impurity admixture in plasma. D inventory achieved values in the 1020 D/m2 range after plasma exposure with high fluences of up to 1 × 1026 D+/m2. In pure and mixed plasmas, the majority of D was trapped in the steel bulk. The Kr and Ar seeding of D plasma resulted in the population of multiple already existing D trapping sites. A similarity of D desorption spectra suggests that D trapping in P92 follows the same mechanism as in EU’97. Kr and Ar seeding mostly contributed to the surface sputtering of the steel samples, yielding less D retention due to the material loss.

Molecular Dynamics Simulation of Physical Sputtering of Nanoporous Silicon-Based Materials with Low Energy Argon

The process of the physical sputtering of the (001) surface of continuous and nanoporous crystalline silicon by 100- and 200-eV Ar ions is simulated using the molecular dynamics method. The features of the process in porous materials are revealed. The dependences of the sputtering yield on the fluence and energies of incident ions are obtained. The structural changes under ion bombardment are described. The dissimilarity between the sputtering mechanisms for materials differing in pore radii and the degree of porosity is demonstrated.

Simulation of cathode surface sputtering by ions and fast atoms in Townsend discharge in argon-mercury mixture with temperature-dependent composition

The mixture of argon and mercury vapor is used as the background gas in different types of gas discharge illuminating lamps. The aim of this work was development of a model, describing transport of electrons, ions and fast atoms in the one-dimensional low-current gas discharge in argon-mercury mixture, and determination of the dependence of their contributions to the cathode sputtering, limiting the device service time, on the temperature.For simulation of motion of electrons we used the Monte Carlo method of statistical modeling, whereas the ion and metastable excited atom motion, in order to reduce the calculation time, we described on the basis of their macroscopic transport equations, which allowed to obtain their flow densities at the cathode surface. Then, using the Monte Carlo method, we found the energy spectra of ions and fast atoms, generated in collisions of ions with mixture atoms, at the cathode surface and also the effective coefficients of the cathode sputtering by each type of particles.Calculations showed that the flow densities of argon ions and fast argon atoms, produced in collisions of argon ions with slow argon atoms, do not depend on the temperature, while the flow densities of mercury ions and fast argon atoms generated by them grow rapidly with the temperature due to an increase of mercury content in the mixture.There are represented results of modeling of the energy spectra of ions and fast atoms at the cathode surface. They demonstrate that at low mercury content in the mixture of the order of 10–3 the energies of mercury ions exceed that of the other types of particles, so that the cathode is sputtered mainly by mercury ions, and their contribution to sputtering is reduced at a mixture temperature decrease.

Correlative Microscopy in 3D: Helium Ion Microscopy-Based Photogrammetric Topography Reconstruction Combined with in situ Secondary Ion Mass Spectrometry.

The chemical or elemental analysis of samples with complex surface topography is challenging for secondary ion mass spectrometry (SIMS), if the three-dimensional structure of the sample is not taken into account. Conventional 3D reconstruction of SIMS data assumes a flat surface and uniform sputtering conditions, which is not the case for many analytical applications involving micro- and nanosized particles, composites, or patterned materials. Reliable analysis of such samples requires knowledge of the actual 3D surface structure to correctly reconstruct the SIMS 3D maps. To this end, we introduce the use of photogrammetric 3D topography reconstruction from scanning helium ion microscopy (HIM) correlated with in situ SIMS data for the reconstruction of 3D SIMS data. The HIM and SIMS data are acquired under in situ conditions in a Zeiss ORION NanoFab HIM using a novel SIMS analyzer. We successfully tested the applicability of the approach to generate 3D models of different samples and show that the combination of SIMS and 3D topography is able to provide insights into the influence of the sample topography in a single instrument and with a single ion column and hence without the need for ex-situ sample analysis or additional instrumentation. These findings offer a path toward ion-based correlative 3D spectromicroscopy (3D-HIM-SIMS) and suggest that many combinations of charged particle based P3D (SEM, HIM) and analytical microscopy techniques, such as SIMS, energy-dispersive X-ray spectroscopy (EDX), or ionoluminescence/cathodoluminescence (IL/CL), can be used for correlative microscopy in 3D.

An ion-beam surface sputtering approach to the quest for lead-free metal halide perovskite for solar cells

Abstract Metal halide perovskites have been the subject of intense theoretical and experimental research in recent years, due to their huge potential over their silicon-based counterparts for tunable optoelectronic applications in high-tech device innovation. The current best perovskite for solar cell applications, with a power conversion efficiency of 22%, methylammonium lead iodide (CH3NH3PbI3), is toxic due to the presence of lead and is therefore harmful in solar cell applications despite its low concentration in solar cells. Hence, research exploits are geared towards perovskites without lead. Unfortunately, this has taken back the gains in PCEs by about 70%, and a lot is being done for improvement. In this paper, a new approach to these studies is introduced by performing Monte Carlo simulations of ion-beam sputtering of lead and tin perovskites, as well as other promising candidate materials, in order to throw some light on their potentials for higher efficiencies in photovoltaic applications. The sputtering characteristics of six promising perovskites, including lead perovskite and lead-substituted perovskites, were compared. The results showed a remarkable exhibition of similar sputtering characteristics of linear projected ion range for Pb and Sn, with a maximum sputter yield around 78° ion incidence. The results also indicated a correspondence between the sputtering characteristics and PCE.

Study of the properties of thin Li films and their relationship with He plasmas using ion beam analysis in the DIONISOS experiment.

Plasma facing component (PFC) conditioning dramatically affects plasma performance in magnetic confinement fusion experiments. Lithium (Li) has been used in several machines to condition PFC with subsequent improvements to plasma performance. Multiple studies have investigated the interactions of Li with deuterium (D) and oxygen (O) in order to ascertain the mechanisms behind the enhanced plasma performance. Ion Beam Analysis (IBA) is a useful tool to interrogate PFC surfaces as they interact with plasmas. Dynamics of ion implantation and sputtering of surfaces (DIONISOS) is a linear plasma device, capable of generating discharges with fluxes ∼1021 m-2 s-1 and Te ∼6 eV, coupled to an ion accelerator. DIONISOS is capable of analyzing samples using Elastic Recoil Detection (ERD) and Rutherford Backscattering Spectroscopy (RBS) during plasma exposures. The facility has been equipped with a Li deposition system for evaporation of thin coatings on different substrates. The evaporator enables real time ERD and RBS measurements of deposition and erosion of Li coatings on different substrates and the interaction of the Li with the vacuum and plasma. Considerations for ERD, e.g., ion species, energy, and data acquisition frequency, are presented. This work is the basis for further investigation of He, H, and D retention in solid and liquid Li.

Fluence dependent changes of surface morphology and sputtering yield of iron: Comparison of experiments with SDTrimSP-2D

Abstract The influence of surface morphology modifications on the sputtering yield of thin Fe films by monoenergetic Ar ions is studied by using a highly sensitive quartz crystal microbalance (QCM) technique. The morphology changes are induced by prolonged sputtering up to a total Ar fluence of 8 × 1021 m−2. Atomic force microscopy (AFM) measurements are performed to analyse the sample topography before and after irradiation and to determine surface roughness parameters. Numerical modelling with the codes SDTrimSP and SDTrimSP-2D are performed for comparison. Our investigations show that by using the local distribution of projectile impact angles, as derived from AFM measurements, as well as the elemental composition of the samples as an input to the codes SDTrimSP and SDTrimSP-2D the agreement between experiment and simulations is substantially improved.

Formation of (), (n = 1, 2), and ArCu+ ions during sputtering of a copper surface by low-energy Ar+ ion bombardment in a dilute argon atmosphere

Formation of monoatomic Ar+ and Cu+, diatomic , ArCu+, and , and triatomic ions during 500 eV Ar+ ion bombardment of a copper surface in a dilute argon atmosphere was investigated by means of energy-resolved mass spectrometry. Energy spectra of (n = 1, 2), (), and ArCu+ ions show distinct features which are related to the specific formation processes taking place in the plasma region and during ion bombardment of the Cu cathode.

Solar wind sputtering of wollastonite as a lunar analogue material – Comparisons between experiments and simulations

The sputtering of wollastonite (CaSiO3) by solar wind-relevant ions has been investigated experimentally and the results are compared to the binary collision approximation (BCA) codes SDTrimSP and SRIM-2013. Absolute sputtering yields are presented for Ar projectiles as a function of ion impact energy, charge state and impact angle as well as for solar wind H projectiles as a function of impact angle. Erosion of wollastonite by singly charged Ar ions is dominated by kinetic sputtering. The absolute magnitude of the sputtering yield and its dependence on the projectile impact angle can be well described by SDTrimSP as long as the actual sample composition is used in the simulation. SRIM-2013 largely overestimates the yield especially at grazing impact angles. For higher Ar charge states, the measured yield is strongly enhanced due to potential sputtering. Sputtering yields under solar wind-relevant H+ bombardment are smaller by two orders of magnitude compared to Ar. Our experimental yields also show a less pronounced angular dependence than predicted by both BCA programs, probably due to H implantation in the sample. Based on our experimental findings and extrapolations to other solar wind ions by using SDTrimSP, we present a model for the complete solar wind sputtering of a flat wollastonite surface as a function of projectile ion impact angle, which predicts a sputtering yield of 1.29 atomic mass units per solar wind ion for normal impact. We find that mostly He and some heavier ions increase the sputtering yield by more than a factor of two as compared to bombardment with only H+ ions.

Formation of Porous Germanium Layers by Silver-Ion Implantation

We propose a method for the formation of porous germanium (P-Ge) layers containing silver nanoparticles by means of high-dose implantation of low-energy Ag+ ions into single-crystalline germanium (c-Ge). This is demonstrated by implantation of 30-keV Ag+ ions into a polished c-Ge plate to a dose of 1.5 × 1017 ion/cm2 at an ion beam-current density of 5 μA/cm2. Examination by high-resolution scanning electron microscopy (SEM), atomic-force microscopy (AFM), X-ray diffraction (XRD), energy-dispersive X-ray (EDX) microanalysis, and reflection high-energy electron diffraction (RHEED) showed that the implantation of silver ions into c-Ge surface led to the formation of a P-Ge layer with spongy structure comprising a network of interwoven nanofibers with an average diameter of ∼10–20 nm Ag nanoparticles on the ends of fibers. It is also established that the formation of pores during Ag+ ion implantation is accompanied by effective sputtering of the Ge surface.

COMPUTER SIMULATION OF NANO-DIMENSIONAL EDUCATION STRUCTURES ON THE SURFACE OF A MONOCRYSTAL AT THE SLIDE ION BOMBING

This work deals with the computer simulation of low- and medium energy (E0=0.5÷10 keV) N+, Ne+, Ar+, Kr+, Be+ и Se+ions sliding collisions on the surface of a Cu(100), Ag(110), Si(001), SiC(001) and GaAs(001) solids, and of the accompanying effects, namely, scattering, sputtering and surface implantation. It has been shown that under these conditions the inelastic energy losses become predominant over the elastic ones. The anomalous energy losses observed experimentally at the grazing ion scattering by the single crystal surface were explained. It has been shown that from the correlation of the experimental and calculated energy distributions of the scattered particles, one may determine a spatial extension of the isolated atomic steps on the single crystal surface damaged by the ion bombardment. Results obtained can be also used to study short-range order in alloys undergoing ordering. Dissociative and non-dissociative desorption of adsorbed molecules were simulated. It was shown that at grazing ion bombardment the intensive nondissociative desorption of adsorbed molecules is possible. A preferential emission of Cu atoms in the case of Cu3Au (001) surface sputtering is observed. It was shown that in the case of grazing ion bombardment the layer-by-layer sputtering is possible and its optimum are observed within the small angle range of the glancing angles near the threshold sputtering angle. The obtained results allow to select the optimum conditions for obtaining implanted depth distributions with demanded shape in narrow near-surface region (5–10 atomic layers) of crystals. The highly sensitive layer-by-layer analysis method was proposed on the basis of layer-by-layer sputtering mechanism.

Spacecraft-plasma-debris interaction in an ion beam shepherd mission

This paper presents a study of the interaction between a spacecraft, a plasma thruster plume and a free floating object, in the context of an active space debris removal mission based on the ion beam shepherd concept. The analysis is performed with the EP2PLUS hybrid code and includes the evaluation of the transferred force and torque to the target debris, its surface sputtering due to the impinging hypersonic ions, and the equivalent electric circuit of the spacecraft-plasma-debris interaction. The electric potential difference that builds up between the spacecraft and the debris, the ion backscattering and the backsputtering contamination of the shepherd satellite are evaluated for a nominal scenario. A sensitivity analysis is carried out to evaluate quantitatively the effects of electron thermodynamics, ambient plasma, heavy species collisions, and debris position.

Elucidation of ALD MgZnO deposition processes using low energy ion scattering

Low energy ion scattering (LEIS) provides an analytical tool for probing the surface composition and structure on the angstrom to nanometer scale. These length scales are central to the growth and processing of ultrathin films produced by atomic layer deposition (ALD). Here, the authors present the application of LEIS to the elucidation of ALD deposition processes and in particular how it provides information about growth parameters including the growth per cycle (GPC), the nature of the film–substrate interfaces, and adatom incorporation into the growing film. The deposition of varying thickness zinc oxide films and the composition of magnesium-doped zinc oxide films are used as model systems. LEIS has been used to investigate the GPC of ZnO using two approaches, namely, static and dynamic measurements. The static approach exploits inelastic energy loss processes to estimate the GPC of different thicknesses of ZnO films. The dynamic approach measures the GPC via a combination of LEIS surface analysis and sputter depth profiling. The measurement of GPC using these two methods is compared with spectroscopic ellipsometry. The adatom incorporation of Mg into the ZnO matrix is measured using a dynamic LEIS process, and the variation of Mg incorporation is discussed as a function of the varying ALD cycle fractions of Mg and ZnO used to deposit MgxZn1-xO films in the range of 0 < x < 1.